According to conventional practice, the surfaces of electrodes used in alchemical cells are prepared using abrasive media blasting, such as sandblasting. Sandblasting employs high pressure air and particulate abrasive matter to cut the surface of the target electrode. There are a number of disadvantages associated with conventional sandblasting processes as discussed below.
Conventional sandblasting processes involve a high degree of risk to the worker. Generally, Silica sand is utilized as the abrasive material for electrochemical reasons. Silica dust, however, presents health hazards and environmental concerns. Other materials, such as steel shot, slag, and walnut shells, tend to produce inferior electrode surfaces and, like Silica, have limited life spans. When these materials are utilized as the abrasive material, they are exposed to one of the following phenomena or a combination of both: First, the cutting surfaces of the material may fracture, thereby reducing the effectiveness of the cut. Second, the material may pick up a coating of lead during the blasting process which, in turn, blunts the cutting surfaces of the material, thereby reducing the effectiveness of the cut. In turn, both phenomena reduce the usability (i.e., lifespan) of the abrasive material. In addition, the particulates emitted into the atmosphere during sandblasting are also hazardous, thereby further endangering workers.
Conventional sandblasting also produces spent materials which require costly disposal operations. Once the abrasive material has met the end of its life span, it must be safely disposed. Due to the level of lead and silica contamination produced during sandblasting, the spent material is non-recyclable and must either be disposed of as hazardous waste or exposed to further processing to remove the hazardous materials—both of which are costly. In addition, workers involved in transporting the materials are further exposed to hazardous material.
In addition, the U.S. Environmental Protection Agency (E.P.A.) has lowered the ambient air lead standard to 0.15 μg/m3 from 1.2 μg/m3. Conventional sandblasting operations cannot readily meet this standard. Currently, sandblasting is done in rooms with large doors for ease of loading. As the material is blasted, it is propelled throughout the room. Air systems are employed to capture much of this material and filter it out, but inevitably some material avoids capture. The escaped material settles out and needs to be vacuumed up before it gets reintroduced to the air, or transported outside of the blasting room. The addition of a negative pressure system can help to reduce this problem, but not eliminate it. Additionally, the blast media eventually must be disposed; however, it is contaminated with lead, thereby requiring disposal as a hazardous waste which adds further cost to the operation.
The abrasive grit itself also gives rise to concern. During sandblasting, the grit can become embedded in the lead electrode sheets. Once embedded, the grit can interfere with the customer's tank house chemistry, possibly affected the end product.
Conventional sandblasting also requires a costly skilled workforce. If the workers are not sufficiently skilled, sandblasting can result in uneven surface finishes, thinning, or even warping of the electrodes. Even given sufficiently skilled workers, these problems may still arise due to human error.
Once the electrodes have been produced using conventional sandblasting, their usefulness is also limited. In electrowinning tanks, for example, when the lead anode is submerged in the tank liquor, the chemical reaction results in a layer of lead oxide forming on the surface of the anode, which helps to protect the anode from corrosion. Due to the characteristics of the surface produced by sandblasting, the protective lead oxide layer has difficulty adhering to the anode surface and takes some time to form, thereby allowing corrosion to begin and significantly reducing the life span of the anode. In addition, since the lead oxide layer has difficulty adhering to the anode, some particles fall to the bottom of the tank housing. Over time, this results in a high amount of sludge forming at the bottom of the tank, which calls for costly periodic cleanings.
In view of the foregoing, there is a need in the art for an electrode surfacing process which removes the need for a skilled labor workforce and the associated high probability of defective electrodes, and reduces environmental hazards and worker safety concerns, and the costs associated therewith. There is also a need in the art for an electrode surfacing process which meets new E.P.A. standards. In addition, there is a need in the art for an electrode having improved surface adherence capability, thereby resulting in a more cost efficient and useful electrode.